What is the best way to automate screenshotting of specific elements on a page?

[ghxstweb]

He @simonw , thanks for designing great tool! I wanted to ask if you might have any suggestions on the best way to automate taking a serial (and separate) screenshots of an element with a specific class designation, and save them all separately as PNGs in a destination folder. I am the maintainer of pdf_lab_js and I wanted to integrate your tool in a CLI, or script, that basically accesses the rendered document (which is rendered on the browser on a local server) and it pulls PNGs of the document directly. Any insight would be great!

Thanks!